1. Field of the Invention
The present invention relates to an active control of a helicopter for the enhancement of stability, improvement of operation characteristics, reduction of vibration and an automatic control of hovering.
More particularly, the invention relates to an active control mechanism of the helicopter which is capable of changing the rotor damping and/or control power of the helicopter into the optimum values corresponding to the desired flight conditions, satisfying the contradictory characteristics of stability and quick mobility, and further, operating automatically at hovering and so on.
2. Description of the Prior Art
The operation control mechanism of a helicopter is basically unchanged since its invention, and the rotation of the rotor which is a matter of course is dominant in every respect.
That is to say, many benefits have occurred from its high degree of freedom in flight characteristics, while various problems have arisen in its dynamic instability and flight characteristics at hovering and low speed cruising due to the lack of means to maintain self-stability.
Also, the operability of the helicopter is said to be determined by the factors of control power and rotor damping, values which could be never improved particularly.
Conventionally, in order to increase the control power, a rigid rotor without a flapping hinge has been proposed, or for increasing the damping power, a so-called stabilizing bar and a servo-control rotor have been devised as disclosed, for example, in U.S. Pat. No. 3,050,276.
However, both techniques are still far from substantially solving such problems.
The helicopter was considered to be inherently unstable, thus forcing an excessive operating load on the pilot. Therefore, ever since the birth of helicopter, mechanical or electrical stabilizing mechanisms have been incorporated.
As a most popular electrical stabilizing mechanism, there is a stability augmentation system (SAS) wherein an actuator is arranged in a cyclic control rod or a main operating system in series, so that by an angular velocity signal of the inclined angle of a fuselage detected with various sensors, damping is given and controlled. Thereby, stability was believed to be enhanced, but the operability, in particular, a high mobility was yet to be satisfied at the same time.
Recently, due to changes in traffic and transporting conditions, the helicopter is required to have a high mobility and responsiveness in addition to a high stability.
Therefore, a control augmentation system (CAS) designed to provide both stability and operability, and a stability and control augmentation system (SCAS) combined with SAS have been developed to exclude the steering signal of the pilot from the SAS output.
Also, a device for obtaining the static stability is proposed to arrange the actuator in the operating system in series and actuate it as a function of the velocity or steering position.
Moreover, as to an attitude control, the difference between assumed and actual attitude angles of the fuselage is normally controlled by the feedback, and tending to be, together with the SAS, etc., integrated in an automatic operating mechanism, a so-called auto-pilot.
For example, U.S. Pat. No. 3,520,498 relates to "the stabilization of aircraft rotor systems having cyclic pitch, and more particularly to the generation of a signal representing rate of the change in the attitude of the rotor shaft relative to a first control axis for introducing cyclic pitch relative to a second control axis".
However, in either a conventional stability or a control augmentation system, the other mechanism is used together on the basis of SAS, resulting in a limited effect and a poor real time response corresponding to the changes of actual flight conditions, therefore the development of a more superior system and an operability which is variable in response to the desired flight conditions have been earnestly desired.